Sprayable liner for supporting the rock surface of a mine

ABSTRACT

The invention provides a liner which is the product of reaction of a (a) hydrophilic prepolymer bearing isocyanate groups; and (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.

FIELD OF THE INVENTION

[0001] The invention relates to an elastomeric polymeric film that canbe used, for example, to assist in protecting from rock bursts in amine. The invention also relates to a method for providing support torock surfaces.

BACKGROUND OF THE INVENTION

[0002] Underground mining requires support of the roof and walls of themine to prevent injury due to rock bursts. Several materials have beenused for this purpose, including shotcrete, wire mesh, as well assprayable liner compositions. Both shotcrete and wire mesh are difficultto handle and apply in the underground mines, more particularly in deepmining applications. The application of shotcrete/gunite is laborintensive and the linings are brittle, are lacking in significanttensile strength, and toughness, and are prone to fracturing uponflexing of the rock during mine blasting. More significantly,shotcrete/gunite develops its desired minimum strength of 1 Mpa onlyslowly. The sprayable liners that develop strength quickly are toxicduring spray application, whereas, liners that are have low toxicityduring spray application are not flexible enough and require more thanfour hours to develop the minimum strength desired to be useful in themining environment. As such a tough, flexible, quick strengthdevelopable liner system having low toxicity is in need.

[0003] Calder et al, in U.S. Pat. No. 5,716,71 1 have described a twopart polyurethane composition preferably containing a layer of inorganicmaterial.

[0004] Sengupta et al. in Canadian Patent Application No. 2,107,496describes an in situ geosynthetic barrier as a secondary containmentbarrier for a petroleum-oil-lubricant facility.

[0005] JP 57104798, assigned to Takenaka Komuten, describes a waterbarrier structure for tunnels using water reactive grout composed ofisocyanate and curing agent.

[0006] DE 3343212 assigned to MC-Bauchemie Muller describes twocomponent polyurethane sealant linings for tunnels based on a sprayablepolyether and liquid crude isocyanate.

[0007] U.S. Pat. No. 4,142,030, assigned to Bayer, describes ainorganic-organic polyurethane-poly-silica gel composite which is madeby mixing an organic polyisocyanate, an aqueous silicate solution and/oran aqueous silica sol and an organic compound with at least oneNCO-reactive H-atom and at least one ionic and/or non-ionic hydrophilicgroup allowing the resultant system to react completely, which can besprayed on walls in mines to prevent accidents.

[0008] Gasper in U.S. Pat. No. 4,476,276 has described a sealingcomposition containing up to 60% by weight fillers by reactingwater-soluble polyurethane prepolymer with water containing latex thatis capable of preventing leakages.

[0009] The effect of spraying either monomeric polyisocyanate and/or apolymer containing a high percent (about 8 to 15% or more) of isocyanategroups and reacting these compounds with either a hydroxy- oramine-containing polyol, as described in the prior art, especially in aconfined area, such as an underground mine, can be very serious from atoxicity standpoint, as some isocyanate is released into the atmosphereand can be ingested. To minimize ingestion a water curtain is normallyprovided, which is an additional, undesirable step.

SUMMARY OF THE INVENTION

[0010] The present invention minimizes the above-described toxicityeffects by lowering the amount of free isocyanate groups in thecomposition used to form a coating on a surface, and by utilizing alarge amount of water-borne polyurethane dispersion. In addition, themethod of the present invention does not generate measurable heat. Thisresult, again, is advantageous, as heat encourages volatilization, andconsequent ingestion of isocyanate and of any other toxic agentspresent.

[0011] The invention provides a liner which is the product of reactionof:

[0012] (a) a hydrophilic prepolymer bearing isocyanate groups; and

[0013] (b) a water-borne polyurethane dispersion, the polyurethanebearing groups that are reactive to isocyanate groups.

[0014] In another aspect, the invention provides a method for providinga surface with a liner, the method comprising

[0015] (I) applying to the surface

[0016] (a) a hydrophilic prepolymer bearing isocyanate groups, and

[0017] (b) a water-borne polyurethane dispersion, the polyurethanebearing groups that are reactive to isocyanate groups; and

[0018] (II) allowing the applied components (a) and (b) to react to formthe liner.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred features of the polyurethane used in component (b)include (i) that it has a molecular weight in the range of from about100,000 to about 700,000; (ii) that it is in the form of particles of asize from about 30 to about 1000 nm, more preferably from about 30 toabout 500 nm; (iii) that a film prepared from the polyurethane has amodulus of at least about 6.89 MPa at 100% elongation, more preferablyabout 13.79 MPa at 100% elongation, and most preferably about 20.69 Mpaat 100% elongation; (iv) that a film prepared from the polyurethane hasa value of T_(g) greater than about 40° C., more preferably greater thanabout 50° C.; and (v) that the polyurethane is used as a dispersion inwater containing no co-solvent.

[0020] The groups on the polyurethane which are reactive to isocyanategroups are preferably alcohol, or amino groups, more preferably primaryamino groups.

[0021] The product of the reaction of hydrophilic prepolymer and thepolyurethane dispersion is a gelatinous mass, as the hydrophilicmoieties of the hydrophilic prepolymer absorb water that is the vehicleof the polyurethane. This gelatinous mass is sometimes referred to as agel or hydrogel, and it can be used, for example, as a liner in a mine.Reaction times to convert the prepolymer to the gel can be on the orderof less than a minute to several hours. The formed gel generallydevelops a minimum strength of about 1 Mpa within about four hours,preferably within about 2-4 hours. The tensile strength of the linerafter it is completely formed (fully cured) is preferably about 6-12Mpa, more preferably about 10-12 Mpa at room temperature. When thecomposition of the present invention is applied at colder temperaturesor under high humidity conditions, longer periods of time can berequired for the composition to become fully cured.

[0022] The weight ratio of the component (a) to component (b) ispreferably in the range of from about 1:3 to about 1:10, more preferablyfrom about 1:4 to about 1:7 and most preferably from about 1:5 to about1:6. However, to increase the hydrophobicity of the resulting liner itis desirable to use as little of component (a) as possible.

[0023] Some of the isocyanate groups of the hydrophilic prepolymer canreact with water to form carbamic acid moieties which immediatelydecarboxylate to generate amines. These amines can then react with otherisocyanate groups to lead to crosslinking of the prepolymer. Water isabsorbed into the ethylene oxide matrix of the product leading toformation of the gel. The liner of the present invention is preferablygas-tight and flexible. The liner of the invention preferably has anelongation at break of from about 100 to about 1000%, more preferablyfrom about 100 to about 800%, most preferably from about 200 to about400%. The resulting liner is, therefore, preferably, a water-insoluble,cross-linked, water-containing gelatinous mass having a high degree ofelasticity.

[0024] The liners produced according to the invention can be used tosupport rock surfaces in a mine. For such applications, the liners arepreferably thick, around 0.5 mm to 6 mm, when formed completely andafter removal of aqueous solvent.

[0025] Water-borne polyurethanes and processes for their preparation areknown. Examples of such water-borne polyurethanes and such processes aredescribed in “Advances in Urethane Science and Technology”, WaterbornePolyurethanes; Rosthauser, James W.; Nachtkamp, Klaus; 1989, Vol. 10,pp. 121-162, Mobay Corp., Pittsburgh, Pa., the description of which isincorporated herein by reference. The water-borne polyurethanedispersion can be made, for example, according to one of the methodsdescribed in this reference. Other suitable examples of water-bornepolyurethane dispersions and processes for their preparation aredescribed in U.S. Pat. No. 5,312,865; U.S. Pat. No. 5,555,686; U.S. Pat.No. 5,696,291; U.S. Pat. No. 4,876,302, and U.S. Pat. No. 4,567,228. Thedisclosures of these patents are incorporated herein by reference. Apreferred method for forming the water-borne polyurethane dispersion isthe prepolymer method.

[0026] The water-borne polyurethane dispersion is preferably hydrophobicin nature to reduce or prevent hydrolysis of its polymeric backbone. Thehydrolytic resistance of the polyurethane polymer can depend on thebackbone of the polyol that is used as a precursor in its synthesis.Normally adipic acid based polyester polyols are more resistant tohydrolysis than phthalate-based polyester polyols. The polyurethanedispersions made from prepolymers having polyols based on polycarbonateor dimer acid diol have higher hydrolytic resistance.

[0027] A suitable water-borne polyurethane polymer is NeoPac™ 9699, awater-borne urethane/acrylic based polyurethane (total solids 40%;viscosity 100 cps at 25° C.; elongation 160%, 100% modulus, 26.2 MPa;Tensile, PSI 4400) from Neoresins, Ontario, Canada; HD 2334, a polyetherwater-borne urethane dispersion (Solids 45%; elongation 200%; 100%modulus; 17.24 MPa, tensile; psi 3500) from C. L. Hauthaway & SonsCorporation, Mass., USA; Hybridur™ 540, a polyester-acrylate basedurethane dispersion from Air Products, USA; and Hybridur™ 580, anacrylic-urethane dispersion, from Air Products & Chemicals Inc., Pa.,USA.

[0028] The amount of water present in these commercially availablepolyurethane dispersions ranges from about 50 to 65% by wt. This rangeis normally satisfactory for use in the invention, and no need is seento depart from this range. Use of amounts of water outside of this rangeare, however, within the scope of this invention, and the percentage ofwater can be readily adjusted.

[0029] Other water-borne non-polyurethane polymeric emulsions such asemulsions of acrylic, acrylic styrene, styrene butadiene, vinyl acetate,or acrylic polymers that form a continuous liner film may replace partof the polyurethane polymer dispersion. Examples include Acronal™S-305D, a butyl acrylate/styrene copolymer, from BASF, and Rhoplex™ 2848and Rhoplex™ 2438 (acrylic emulsions from Rohm & Haas Company). However,these emulsions generally reduce the initial (4 hrs) and ultimatetensile strengths, and generally cannot provide the desired strength ofthe resulting liner of at least about 1 Mpa tensile strength withinabout 4 hours, preferably within about two hours.

[0030] The hydrophilic prepolymer is preferably a urethane-containingpolymer bearing isocyanate groups and can be formed by reacting ahydrophilic polyol with an excess of polyisocyanate. This step isfollowed by purifying the hydrophilic prepolymer of unreactedpolyisocyanate or, preferably, by quenching the unreacted polyisocyanatewith a compound that is reactive to isocyanate groups, so that theprepolymer contains less than about 0.5 weight percent of unreactedpolyisocyanate.

[0031] Unless the amount of unreacted polyisocyanates present in themixture containing the hydrophilic prepolymer is lowered through apurification step, or effectively reduced by, for example, quenching theisocyanate groups of the polyisocyanates, the presence of thepolyisocyanate can result in considerable toxicity. It was surprisinglyfound that by removing or quenching the unreacted polyisocyanatesaccording to the process of the present specification, liners ofsuperior strength were produced. Other advantages include reducedtoxicity, and lowered heat generation.

[0032] The hydrophilic prepolymer can be purified from unreactedmonomeric polyisocyanate by processes and/or methods using, for example,falling film evaporators, wiped film evaporators, distillationtechniques, various solvents, molecular sieves, or organic reactiveregent such as benzyl alcohol. U.S. Pat. No. 4,061,662 removes unreactedtolylene diisocyanate (TDI) from an isocyanate prepolymer by contactingthe prepolymer with molecular sieves. U.S. Pat. Nos. 3,248,372,3,384,624, and 3,883,577 describe processes related to removing freeisocyanate monomers from prepolymers by solvent extraction techniques.It is also possible to distill an isocyanate prepolymer to remove theunreacted diisocyanate according to U.S. Pat. No. 4,385,171. It isnecessary to use a compound which is only partially miscible with theprepolymer and has a higher boiling point than that of the diisocyanateto be removed. U.S. Pat. Nos. 3,183,112, 4,683,279, 5,051,152 and5,202,001 describe falling film and/or wiped film evaporation. Accordingto U.S. Pat. No. 5,502,001, the residual TDI content can be reduced toless than 0.1wt. % by passing the prepolymer at ˜100° C. through a wipedfilm evaporator, while adding an inert gas, especially nitrogen, to thedistillation process to sweep out the TDI. The disclosures of all ofthese references are incorporated herein by reference.

[0033] Unreacted polyisocyanates can be quenched with an amine,preferably a secondary amine, more preferably a monofunctional secondaryamine, an alcohol, for example, an arylalkyl alcohol, preferably in thepresence of a tertiary amine catalyst, such as, triethylamine, or analkoxysilane bearing a functional group that is reactive to isocyanategroups, for example, an amine. The unreacted polyisocyanates are morepreferably reacted with an arylalkyl alcohol, such as benzyl alcohol,used with a tertiary amine. The unreacted polyisocyanates are mostpreferably reacted with an arylalkyl alcohol, such as benzyl alcoholused in conjunction with an alkoxysilane bearing a secondary aminogroup. The unreacted polyisocyanates can be quenched withoutsubstantially affecting the terminal isocyanate groups from thehydrophilic prepolymer.

[0034] Examples of suitable amines include N-alkyl aniline, for example,N-methyl or N-ethyl aniline and its derivatives, diisopropylamine,dicyclohexylamine, dibenzylamine, or diethylhexylamine.

[0035] Example of suitable alcohols include arylalkyl alcohols, forexample, benzyl alcohol, and alkyl-substituted derivatives thereof.

[0036] Examples of suitable silanes include Dynasylan™ 1189(N-(n-butyl)-aminopropyltrimethoxysilane, Dynasylan™ 1110(N-methyl-3-Aminopropyltrimethoxysilane), and Silquest™ A-1170 (bis(trimethoxysilylpropyl)amine available from Osi Co., and Silquest™Y-9669 (N-phenyl)-gamma-aminopropyltrimethoxysilane.

[0037] When alcohols are used to quench the unreacted polyisocyanates,the application of heat is generally required to reduce the reactiontime. Reactions with amines can be conducted, however, at ambienttemperature for a relatively shorter period of time.

[0038] The amount of unreacted polyisocyanates present in the reactionmixture comprising the hydrophilic prepolymer following the reactionwith the amine, alcohol or silane is preferably 0, but can range up toabout 0.5 weight percent.

[0039] A preferred method of purifying the hydrophilic prepolymer (a) isby the method of U.S. patent application Ser. No., filed on even dateherewith, Attorney's Docket No. 57017US002, the disclosure of which isincorporated herein by reference.

[0040] A suitable hydrophilic polyol for use in the preparation of thehydrophilic prepolymer bearing isocyanate groups is a polyether polyolhaving at least two, preferably three, hydroxyl groups, and a numberaverage molecular weight in the range of from about 2,000 to about20,000, preferably about 2,000 to about 5,000, most preferably about4,000 to about 5,000, and having random ethylene oxide units and higheralkylene oxide units in a mol ratio of ethylene oxide (EO) to higheralkylene oxide of 1:1 to 4:1. The higher alkylene oxide can be selectedfrom the group consisting of propylene oxide (PO), butylene oxide,pentylene oxide, hexylene oxide and mixtures thereof. The hydrophilicpolyol is preferably a polyoxyethylene-propylene polyol comprising, forexample, 50 to 70% EO and 30 to 50% PO. A particularly preferredpolyether triol is one comprising approximately 68% EO and approximately32% PO. Alternate ratios of EO:PO can be used in preparing thehydrophilic polyol of the present invention provided that thehydrophilicity of the resulting polyol is not significantly adverselyaffected. These ratios can be determined by routine testing.

[0041] Commercially available polyol precursors useful in making theabove described water-soluble isocyanate-terminated prepolymers are thehydrophilic polyols, e.g., a polyG™ triol, such as “polyG™-83-84”,available from Arch Chemicals. The degree of overall hydrophilicity ofthe prepolymeric mixtures can be modified by varying the ratio ofethylene oxide to propylene oxide in the hydrophilic polyol, or by usingsmall amounts of poly(oxyethylene-oxypropylene) polyols sold under thetrademark “Pluronic”, such as Pluronic-L35, F38, and P46, or hydrophilicpolyols with heteric oxyethylene-oxypropylene chain sold as PolyolFunctional Fluids, such WL-580, WL-600, and WL-1400.

[0042] The hydrophilic prepolymer bearing isocyanate groups can beprepared, for example, by reacting a polyisocyanate with a copolymer ofpolyoxyethylene-propylene polyol using an NCO/OH equivalent ratio ofabout 5:1 to about 1.05:1, preferably a ratio of about 2.0:1 to 2.5:1.The preparation of isocyanate-terminated prepolymers is disclosed in,for instance, U.S. Pat. Nos. 4,315,703 and 4,476,276 and in referencesmentioned in those patents. The disclosures of these patents areincorporated herein by reference. Preferably, aromatic isocyanate isused for its greater reactivity rate than aliphatic isocyanate. Benzoylchloride can be added during prepolymer preparation to avoid sidereactions of polyisocyanate.

[0043] Polyisocyanates that can be used to prepare the hydrophilicprepolymer having isocyanate groups include aliphatic and aromaticpolyisocyanates. The preferred polyisocyanates are aromaticpolyisocyanates. One of the most useful polyisocyanate compounds thatcan be used is tolylene diisocyanate, particularly as a blend of 80weight percent of tolylene-2,4-isocyanate, and 20 weight percent oftolylene-2,6-isocyanate; a 65:35 blend of the 2,4- and 2,6-isomers isalso useable. These polyisocyanates are commercially available under thetrademark “Hylene”, as Nacconate™ 80, and as Mondur™ RD-80. The tolyleneisocyanates can also be used as a mixture with methylene diisocyanate.Other useable polyisocyanate compounds that can be used are otherisomers of tolylene diisocyanate, hexamethylene-1,6-diisocyanate,diphenyl-methane-4,4′-diisocyanate, m- or p-phenylene diisocyanate and1,5-naphthalene diisocyanate. Polymeric polyisocyanates can also beused, such as polymethylene polyphenyl polyisocyanates, such as thosesold under the trademarks “Mondur” MRS, and “PAPI”. A list of usefulcommercially available polyisocyanates is found in Encyclopedia ofChemical Technology by Kirk and Othmer, 2nd Ed., Vol. 12, pages 46, 47,Interscience Pub. (1967).

[0044] Preferably, no solvent is used to dilute the hydrophilicprepolymer. However, a solvent can be used if necessary. Solvents thatcan be used to dissolve the prepolymer are water-miscible, polar organicsolvents that are preferably volatile at the ambient conditions of theenvironment where the sealing composition is to be used. The solventchosen should be such that the resulting solution of prepolymers andsolvent will not freeze at the ambient conditions present in theenvironment where the mixed composition of the invention is to beapplied. For example, where the ambient temperature is about 50° F., asolution of about 60-90 weight percent of prepolymer solids in dryacetone is an effective composition. Other useful water-misciblesolvents include methyl acetate, tetrahydrofuran dimethyl formamideethylene glycol monoethyl ether acetate (sold under the tradedesignation “Cellosolve” acetate), N-methyl pyrrolidone, and diethylacetal, and hydrophilic plasticizers, such as Atpol™ 1120, availablefrom Uniquema, Belgium.

[0045] Other additive ingredients can be included in the composition ofthe present invention. For example, viscosity modifiers can be includedto increase or decrease the viscosity, depending on the desiredapplication technique. Fungicides can be added to prolong the life ofthe gel and to prevent attack by various fungi. Other active ingredientscan be added for various purposes, such as substances to preventencroachment of plant roots, and the like. Other additives that can beincluded in the composition of this invention, include, withoutlimitation, rheological additives, fillers, fire retardants, defoamersand coloring matters. Care should be exercised in choosing fillers andother additives to avoid any materials which will have a deleteriouseffect on the viscosity, reaction time, the stability of the liner beingprepared, and the mechanical strength of the resulting liner.

[0046] The additional filler materials that can be included in thecomposition of the present invention can provide a moreshrink-resistant, substantially incompressible, and fire retardantcomposition. Any of a number of filler compositions have been found tobe particularly effective. Useful fillers include water-insolubleparticulate filler material having a particle size of about less than500 microns, preferably about 1 to 50 microns and a specific gravity inthe range of about 0.1 to 4.0, preferably about 1.0 to 3.0. The fillercontent of the cured composition of the present invention can be as muchas about 10 parts filler per 100 parts by weight cured composition,preferably about 5 parts to about 20 parts per 100, more preferably,about 2 parts to about 5 parts per 100.

[0047] Examples of useful fillers for this invention include expandablegraphite such as Grafguard™ 220-80B or Grafguard™ 160-1SOB (Graftech,Ohio, USA), silica such as quartz, glass beads, glass bubbles and glassfibers; silicates such as talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate; metal sulfates such as calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate; gypsum; vermiculite;wood flour; aluminum trihydrate; carbon black; aluminum oxide; titaniumdioxide; cryolite; chiolite; and metal sulfites such as calcium sulfite.Preferred fillers are expandable graphite, feldspar and quartz. Thefiller is most preferably expandable graphite. The amount of filleradded to the composition of the invention should be chosen so that thereis no significant effect on elongation or tensile strength of theresulting liner. Such amounts can be determined by routineinvestigation.

[0048] When filler is added to the composition of the invention, theresulting liner can also be fire retardant. The liner preferably shouldmeet the fire retardant specifications of CAN/ULC-S102-M88 or ASTM E-84.These tests determine bum rate and the amount of smoke generation.

[0049] The components (a) and (b) of the composition of the inventionare preferably mixed immediately before being applied to a surface. Asan example of the mixing process, components (a) and (b) can be pumpedusing positive displacement pumps and then mixed in a static mixerbefore being sprayed onto a surface. The mixture of the two componentscan then be sprayed onto a substrate with or without air pressure. Themixture is preferably sprayed without the use of air. The efficiency ofmixing depends on the length of the static mixer.

[0050] Objects and advantages of this invention are further illustratedby the following examples, but the particular materials and amountsthereof recited in these examples, as well as other conditions anddetails, should not be construed to unduly limit this invention.

EXAMPLES

[0051] Test Methods:

[0052] Test method ASTM D-638-97 was used for measuring tensile strengthand elongation. The tests were performed using an Instron Model 44R1122with a crosshead speed of 200 mm/min.

[0053] Liners that were made in accordance with the present inventionhave passed the Dynamic Stress Membrane Materials testing. Small-scaletests confirmed that the lining material met the basic requirements setby both the liner manufacturer and members of the mining industry. Forsmall scale testing, the liner material was applied by hand mixingcomponents (a) and (b) of the inventive composition to the surface ofgranite core samples (2 inches (5.1 cm) in diameter and 4 inches (10.2cm) long) leaving a 6 mm gap at each end. A leading mining companysupplied the granite cylinders. A crush test was carried out at GolderAssociates, in London, Ontario, after the samples were left for 4 hoursand 24 hours at room temperature. Force was applied on the cylinders bya compressive load using a soft, uncontrolled testing machine tomaximize the potential energy available to sustain a violent type offailure of the cylinders. The granite cylinders were failed withoutdamaging the applied liner on the cylinders.

[0054] Large granite cylinders (7.5 inch (about 19 cm) in diameter and19 inch (about 48 cm) long) were sprayed using a pump system and mixedin a static mixer with two different liner compositions using threedifferent thicknesses. These tests were carried out in Sudbury, Ontarioin CANMET Lab. Again, the cylinders were crushed without affecting theapplied liners.

[0055] Prepolymer 1:

[0056] A general description of prepolymer preparations that can be usedto prepare prepolymer A is given in U.S. Pat. No. 4,476,276, thedisclosure of which is incorporated by reference, especially thepreparation of prepolymers A, B and C of U.S. Pat. No. 4,476,276.

[0057] An amount of benzoyl chloride 0.04% (based on the total amount ofpolyol and tolylene diisocyanate (TDI)) was blended at room temperatureunder an inert atmosphere with 1 equivalent of polyether triol (acopolymer of ethylene oxide and propylene oxide sold under the tradedesignation polyG-83-34, mol. wt. 5400, available from Arch Chemicals),thereafter, 2.4 equivalents of an 80:20 mixture of 2,4 tolyenediisocyanate: 2,6 tolylene diisocyanate (Mondur™ TD-80 available fromBayer Corporation, USA) was added to the resultant mixture withagitation, producing a moderate exotherm that was maintained at 80-85°C. until the reaction was completed. The solution of the prepolymer wasthen cooled to room temperature. The solution contained prepolymershaving on average 3.0 to 3.2 weight percent isocyanate groups, and1.2-2.4 weight percent monomeric TDI, as determined by NMR techniques.

[0058] Prepolymer 2:

[0059] In a 3-necked 2 L round bottom flask, equipped with a mechanicalstirrer and a thermometer, 1271.3 g of Prepolymer 1 was added under anargon atmosphere, 98.1 g (30 molar percent with respect to the total NCOgroups in Prepolymer 1) of Silquest™ A-1170 bis(trimethoxysilylpropyl)amine (available from Osi Co.) was added dropwiseto the prepolymer at 25° C. under argon and with stirring (250 rpm). Thereaction was exothermic causing a 0-10° C. increase in temperature. Thereaction mixture was collected after 2 h. The monomeric TDI content wasfound to be below 0.5 weight percent, as determined by NMR.

[0060] Prepolymer 3:

[0061] In a 3-necked 2 L round bottom flask, equipped with a mechanicalstirrer and a thermometer, 1280.0 g of Prepolymer 1 and 320.0 g of dryacetone were added under argon atmosphere. 134.8 g (40 molar percentwith respect to the total NCO groups in the prepolymer of Example 1) ofSilquest™ A-1170 bis (trimethoxysilylpropyl)amine was added dropwise tothe solution at 25° C. under argon and with stirring (900 rpm). Thereaction mixture was collected after 2 h. The monomeric TDI content wasfound below 0.1 weight percent, as determined by NMR.

[0062] Prepolymer 4:

[0063] In a 3-necked 250 ml round bottom flask, equipped with amechanical stirrer and a thermometer, 205.9 g of Prepolymer 1) ofN-ethyl aniline was then added to the prepolymer while stirring at 25°C. The mixture was collected after 2 h. The monomeric TDI content wasfound to be below 0.2 weight percent, determined by NMR.

[0064] Prepolymer 5:

[0065] In a 3-neck round bottom flask, equipped with a mechanicalstirrer and a thermometer, 200 g of Prepolymer 1 was added under argon.2.74 g (15 molar percent with respect to the total NCO groups inPrepolymer 1) of N-ethyl aniline was added dropwise to the prepolymer at25° C. under argon and with stirring (250 rpm). The reaction was kept atroom temperature for 2 h. Then 7.52 g (15 molar percent with respect tothe total NCO groups in the prepolymer #1) Silquest™ A-1170 bis(trimethoxysilylpropyl)amine was added to the mixture under argon andwith stirring. The reaction was kept at room temperature for 2 h beforecollection. The monomeric TDI content was found to be below 0.3 weightpercent, as determined by NMR.

[0066] Prepolymer 6:

[0067] In a 3-neck 250 ml round bottom flask, equipped with a mechanicalstirrer and a thermometer, 201.0 g of Prepolymer 1 was added underargon. 2.45 g (15 molar percent with respect to the total NCO groups inPrepolymer 1) of benzyl alcohol was added to the prepolymer under argon.The temperature was then raised to 85C. and the reaction was carried outfor 2 h. After the reaction mixture was cooled to room temperature, 7.52g (15 molar percent with respect to the total NCO groups inPrepolymer 1) Silquest™ A-1 170 bis (trimethoxysilylpropyl)amine wasadded the mixture under argon and stirring. The reaction was kept atroom temperature for 2 h before collection. The monomeric TDI contentwas found below 0.2 weight percent, as determined by NMR.

Examples 1-5

[0068] Examples 1-5 provide data for liners formed using NeoPac™ 9699polyurethane dispersion and different prepolymers. The samples were madeby quickly injecting 4.0 g of a prepolymer to 20 g of NeoPac™ 9699 (40%)solid polyurethane dispersion (from NeoResin Canada) followed by mixingthe two components with a spatula and spreading the mixture on apolyester film to a thickness of about 2 to 3 mm. The film surface wasnot smooth due to rapid gelling of the two components. The value oftensile strength of these samples, and the components used to producethem are provided in Table 1. The results indicate that prepolymers witha low amount of monomeric diisocyanate (except for example 9, which isquenched with 40 molar percent mono-functional amine) can provide thesame or better tensile strength as compared to example 7, a liner formedby unmodified prepolymer and polyurethane dispersion. Although Example 9does not demonstrate a tensile strength of 1 Mpa after 4 hours, it doesdemonstrate good results after three days. TABLE 1 Tensile properties at4 h Tensile properties at 3 days Strength Elong. Strength Elong.ExampleNo. Prepolymer (Mpa) (%) (Mpa) (%) 1 1 1.3 305 9.1 550 2 2 1.2* 840* 10.2 330 3 4 0.9 800 10.2 330 4 5 1.6 630 9.2 350 5 6 1.7 660 8.9380

Comparative Examples 1 and 2 and Examples 6-8

[0069] The samples of the following examples and comparative exampleswere made by injecting 4.5 g of prepolymer quickly to 20 g of eachdispersion along with 2 g of fused silica, mixing with spatula andspreading on a polyester film to about thickness of 1.9 mm to 3 mm. Thefilms were not very smooth due to rapid gelling of the two components.The values of tensile strength of these samples, and the components usedto produce them are provided in Table 2. Comparative Example 1 does notuse a polyurethane, and Comparative Example 2 uses a polyurethane thathas a low modulus. TABLE 2 Tensile Strength Example Amount (Mpa) No.Components of Composition (g) After 4 hours C-1 Prepolymer 3 (A) 4.50.34 Vancryl ™ 937 (B) 16.8 Fused Silica 2.0 C-2 Prepolymer 3 (A) 4.50.44 Luphen ™ 3528 (B) 20 Fused Silica 2.0 6 Prepolymer 3 (A) 4.5 1.12Hauthane ™ HD-2334 (B) 18.0 Fused Silica 2.0 7 Prepolymer 3 (A) 4.5 2.08NeoPac ™ R-9699 (B) 20 Fused Silica 2.0 8 Prepolymer 3 (A) 4.5 1.23Hybridur ™ 450 (B) 20 Fused Silica 2.0

[0070]

Example 9

[0071] Liners were made by spraying component A (Prepolymer 4) whichcontains less than 0.1 weight percent of free TDI and component B(Neorez™ R-9699) at a weight ratio of 1:5 with 2 separate pumps andmixing components A & B in a static mixer. The compositions formed weresmooth and showed higher tensile values compared to hand mixed samples.The resulting hand-made and pump-sprayed films were then tested after 4hours to determine their tensile strengths. The strengths were alsoevaluated after 3 days and after several weeks. The results are shown inTable 3. TABLE 3 4 hr.* 1 day* 2 days* 7 days* 7 days** Tensile Strength1.8 9.4 10.9 12 15 (Mpa) % Elongation 700 406 310 252 225

Example 10

[0072] A test was conducted in which a control gel containing no fireretardants and samples containing several different fire retardants wereignited with an open flame. A sample prepared from 4 g of Prepolymer 1or 2, 20 g of component NeoPac™ 9699 and 0.25-1.0 g of the expandablegraphite Grafguard™ 220-80B (Graftech, Ohio, USA) showedself-extinguishability. A sample prepared with the expandable graphiteGrafguard™ 160-150B also demonstrated self-extinguishability but to alower extent.

[0073] Various modifications and alterations to this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims set forth herein asfollows.

We claim:
 1. A liner comprising the product of reaction of: (a) ahydrophilic prepolymer bearing isocyanate groups; and (b) a water-bornepolyurethane dispersion, the polyurethane bearing groups that arereactive to isocyanate groups.
 2. A liner according to claim 1, whereinthe polyurethane used in component (b) has a molecular weight in therange of from about 100,000 to about 700,000.
 3. A liner according toclaim 1, wherein the polyurethane of component (b) is in the form ofparticles of a size from about 30 to about 1000 nm.
 4. A liner accordingto claim 1, wherein a film prepared from the polyurethane used incomponent (b) has a modulus of at least about 14 MPa at 100% elongation.5. A liner according to claim 1, wherein a film prepared from thepolyurethane used in component (b) has a value of T_(g) greater thanabout 40° C.
 6. A liner according to claim 1, wherein the dispersion ofthe polyurethane contains no co-solvent.
 7. A liner according to claim 1which develops a strength of at least about 1 MPa within about 4 hours.8. A liner according to claim 1, wherein said prepolymer is formed byreacting a polymer bearing hydroxyl groups with a polyisocyanate to forma urethane-containing polymer bearing isocyanate groups, which ispurified by removing unreacted polyisocyanate or by quenching unreactedpolyisocyanate with a compound that is reactive to isocyanate groups. 9.A liner according to claim 1, wherein the polyurethane dispersion is inadmixture with a dispersion of an acrylate polymer, an acrylate polymer,an acrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinylacetate polymer.
 10. A liner according to claim 1, wherein the weightratio of component (a) to component (b) is in the range of from about1:3 to about 1:10.
 11. A liner according to claim 1, further comprisingat least one additive selected from the group consisting of rheologicaladditives, fillers, fire retardants, defoamers and coloring matters. 12.A liner comprising (a) the product of reaction of: (1) a hydrophilicprepolymer derived from a polyether polyol and bearing isocyanate groupsderived from an aromatic polyisocyanate; and (2) a water-bornepolyester-acrylate based polyurethane dispersion, the polyurethanebearing groups that are reactive to isocyanate groups; and (b)expandable graphite.
 13. A method for providing a surface with a liner,the method comprising (a) applying to the surface (1) a hydrophilicprepolymer bearing isocyanate groups, and (2) a water-borne polyurethanedispersion, the polyurethane bearing groups that are reactive toisocyanate groups; and (b) allowing the applied components (a) and (b)to react to form the liner.
 14. A method according to claim 13, whereinthe polyurethane used in component (b) has a molecular weight in therange of from about 100,000 to about 700,000.
 15. A method according toclaim 13, wherein the polyurethane of component (b) is in the form ofparticles of a size from about 30 to about 1000 nm.
 16. A methodaccording to claim 13, wherein a film prepared from the polyurethane ofcomponent (b) has a modulus of at least about 14 Mpa at 100% elongation.17. A method according to claim 13, wherein a film prepared from thepolyurethane of component (b) has a value of T_(g) greater than about40° C.
 18. A method according to claim 13, wherein the dispersion of thepolyurethane contains no co-solvent.
 19. A method according to claim 13,wherein the liner develops a strength of at least about 1 Mpa withinabout 4 hours.
 20. A method according to claim 13, wherein saidprepolymer (a) is formed by reacting a polymer bearing hydroxyl groupswith a polyisocyanate to form a urethane-containing polymer bearingisocyanate groups, which is purified by removing unreactedpolyisocyanate or by quenching unreacted polyisocyanate with a compoundthat is reactive to isocyanate groups.
 21. A method according to claim13, wherein the polyurethane dispersion (b) is in admixture with adispersion of an acrylate polymer, an acrylate polymer, anacrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinylacetate polymer.
 22. A method according to claim 13, wherein the weightratio of component (a) to component (b) is in the range of from about1:3 to about 1:10.
 23. A method according to claim 13, furthercomprising at least one additive selected from the group consisting ofrheological additives, fillers, fire retardants, defoamers and coloringmatters.
 24. A method according to claim 13, wherein the thickness ofthe liner is in the range of from about 0.5 mm to about 6 mm.
 25. Amethod according to claim 13, wherein said surface is in a mine opening.26. A method for providing a surface with a liner, the method comprising(a) applying to the surface (1) a hydrophilic prepolymer derived from apolyether polyol and bearing isocyanate groups derived from an aromaticpolyisocyanate; (2) a water-borne polyester-acrylate based polyurethanedispersion, the polyurethane bearing groups that are reactive toisocyanate groups; and (3) expandable graphite; and (b) allowing theapplied components (a) and (b) to react to form the liner.
 27. A mineopening lined with a liner formed by the method of claim
 13. 28. A mineopening lined with a liner formed by the method of claim 26.